Efficiency of a program for family intervention. The present study is aimed to show the efficiency estimation model based on the «Experiential Program for Parents» (Máiquez, Rodrigo, Capote y Vermaes, 1999). This Program was developed in three different community centers placed on Tenerife island, which were dedicated to primary and secondary prevention. The Program is made up of 4 Modules to be treated in 12 meetings. All these meeting were especially useful not only for parents but also for the assistant-mediator to be adviced, thereby analysing the whole process. Generalisability theory allow us to prove the reliability of the design structure used in order to generalize the results. We found that a improvement of the Program application is possible, on the one hand, by increasing moderately the number of categories and, on the other hand, by diminishing the number of observations and registers. In this sense, we reduce Program costs concerning assistant staff while keeping the information level.